scsi: hisi_sas: support the property of signal attenuation for v2 hw

The register SAS_PHY_CTRL is configured according to signal quality.  The
signal quality is calculated by signal attenuation of hardware physical
link. It may be different for different PCB layout.

So, in order to give better support to new board, this patch add support to
reading the devicetree property, "hisilicon,signal-attenuation".  Of course,
we still keep an default value in driver to adapt old board.
Signed-off-by: Xiaofei Tan <tanxiaofei@huawei.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/hisi_sas/hisi_sas_v2_hw.c

@@ -406,6 +406,17 @@ struct hisi_sas_err_record_v2 {
 	__le32 dma_rx_err_type;
 };
 
+struct signal_attenuation_s {
+	u32 de_emphasis;
+	u32 preshoot;
+	u32 boost;
+};
+
+struct sig_atten_lu_s {
+	const struct signal_attenuation_s *att;
+	u32 sas_phy_ctrl;
+};
+
 static const struct hisi_sas_hw_error one_bit_ecc_errors[] = {
 	{
 		.irq_msk = BIT(SAS_ECC_INTR_DQE_ECC_1B_OFF),
@@ -1130,9 +1141,16 @@ static void phys_try_accept_stp_links_v2_hw(struct hisi_hba *hisi_hba)
 	}
 }
 
+static const struct signal_attenuation_s x6000 = {9200, 0, 10476};
+static const struct sig_atten_lu_s sig_atten_lu[] = {
+	{ &x6000, 0x3016a68 },
+};
+
 static void init_reg_v2_hw(struct hisi_hba *hisi_hba)
 {
 	struct device *dev = hisi_hba->dev;
+	u32 sas_phy_ctrl = 0x30b9908;
+	u32 signal[3];
 	int i;
 
 	/* Global registers init */
@@ -1176,9 +1194,28 @@ static void init_reg_v2_hw(struct hisi_hba *hisi_hba)
 	hisi_sas_write32(hisi_hba, AXI_AHB_CLK_CFG, 1);
 	hisi_sas_write32(hisi_hba, HYPER_STREAM_ID_EN_CFG, 1);
 
+	/* Get sas_phy_ctrl value to deal with TX FFE issue. */
+	if (!device_property_read_u32_array(dev, "hisilicon,signal-attenuation",
+					    signal, ARRAY_SIZE(signal))) {
+		for (i = 0; i < ARRAY_SIZE(sig_atten_lu); i++) {
+			const struct sig_atten_lu_s *lookup = &sig_atten_lu[i];
+			const struct signal_attenuation_s *att = lookup->att;
+
+			if ((signal[0] == att->de_emphasis) &&
+			    (signal[1] == att->preshoot) &&
+			    (signal[2] == att->boost)) {
+				sas_phy_ctrl = lookup->sas_phy_ctrl;
+				break;
+			}
+		}
+
+		if (i == ARRAY_SIZE(sig_atten_lu))
+			dev_warn(dev, "unknown signal attenuation values, using default PHY ctrl config\n");
+	}
+
 	for (i = 0; i < hisi_hba->n_phy; i++) {
 		hisi_sas_phy_write32(hisi_hba, i, PROG_PHY_LINK_RATE, 0x855);
-		hisi_sas_phy_write32(hisi_hba, i, SAS_PHY_CTRL, 0x30b9908);
+		hisi_sas_phy_write32(hisi_hba, i, SAS_PHY_CTRL, sas_phy_ctrl);
 		hisi_sas_phy_write32(hisi_hba, i, SL_TOUT_CFG, 0x7d7d7d7d);
 		hisi_sas_phy_write32(hisi_hba, i, SL_CONTROL, 0x0);
 		hisi_sas_phy_write32(hisi_hba, i, TXID_AUTO, 0x2);